Oil sand, as known in the Fort McMurray region of Alberta, Canada, comprises water-wet sand grains having viscous bitumen flecks trapped between the grains. It lends itself to separating or dispersing the bitumen from the sand grains by slurrying the as-mined oil sand in heated water so that the bitumen flecks move into the aqueous phase.
For the past 25 years, the bitumen in McMurray sand has been commercially recovered from oil sand using a heated water process. In general terms, the hot water process that is practiced at applicants plant today involves:
supplying heated water at the mine site; PA1 mixing the dry as-mined oil sand with the heated water at the mine site in predetermined proportions using a device known as a "cyclofeeder", to form a slurry of controlled density having a temperature in the order of 50.degree. C.; PA1 screening the slurry to remove oversize solids too large to be fed to the pipeline; PA1 pumping the slurry to the extraction plant through several kilometers of pipeline; PA1 further diluting the slurry with heated water; and PA1 separating the bitumen from the rest of the oil sand slurry using gravity separation vessels and flotation cells. PA1 dry mining the oil sand; PA1 mixing the as-mined oil sand with water in predetermined proportions near the mine site to produce a slurry having a controlled density in the range 1.4 to 1.65 g/cc and a temperature in the range 20-35.degree. C.; PA1 pumping the slurry from the mine site to the extraction plant through a pipeline having a plurality of pumps spaced along its length; PA1 adding air to the slurry, preferably in the pipeline after the last pump, in an amount up to 2.5 volumes of air per volume of slurry, to form an aerated slurry; and PA1 separating the bitumen from the rest of the oil sand slurry using gravity separation vessels and flotation cells. PA1 a handling very large oil sand slurry flow rates (up to 40,000 U.S. GPM); PA1 handling large lumps up to 4 inches in diameter; PA1 separating out the bulk of solid particles coarser than 44 microns; PA1 handling slurries with varying compositions containing anywhere between 35-60% solids concentration; and PA1 controlling the split in the volumetric flow rate between the light phase and the heavy phase by throttling the effluent flow to optimize separation. PA1 that the lean froth is substantially sand-free; PA1 that the losses of bitumen with the tailings are at acceptable levels; and PA1 that the cylindrical separator vessel can handle high flow rates and lumps up to four inches in diameter. PA1 a closed vessel forming a substantially cylindrical vortex chamber, said vessel having a tangential feed inlet at its first end and a peripheral, preferably tangential, outlet at its second end for the solid effluent; and PA1 a tubular vortex finder extending centrally into the cylindrical vortex chamber at its second end, said vortex finder preferably including a vortex holding disc mounted on the lip of the finder, said vortex finder providing an outlet for the centrate or aerated bitumen phase. PA1 providing a cyclonic separator having a closed vessel forming an elongated, substantially cylindrical vortex chamber, said vessel having a tangential feed inlet at its first end, a centrally positioned vortex finder at its second end for centrate removal and a peripheral, preferably tangential, outlet for solids removal at its second end, said vortex finder preferably having a vortex holding disc extending radially and outwardly from the rim of the vortex finder; PA1 tangentially introducing the slurry into the chamber at its first end to form a rotating vortex; PA1 centrifugally separating the rotating slurry as it advances through the chamber to form an outer layer containing a major portion of coarse solids, an inner core containing a major portion of the aerated bitumen and an intermediate layer of middlings; PA1 separately removing the aerated bitumen core, together with some middlings, through the vortex finder to produce a lean froth stream for further processing; PA1 separately removing the outer layer, together with some middlings, through the peripheral outlet to produce a tailings stream for disposal; and PA1 preferably utilizing more than one cycloseparator in series to minimize bitumen loss in the coarse tailings.
A recent development in the recovery of bitumen from oil sand involves a low energy extraction process (LEE process). The LEE process involves:
In both of the aforementioned processes, much of the conditioning of the oil slurry takes place in the pipeline. Here, the larger lumps of oil sand are ablated and the released bitumen flecks coalesce and attach to air bubbles. At this stage the slurry is commonly referred to as "conditioned slurry". Once the slurry reaches the extraction site, the aerated bitumen is then separated from the rest of the oil sand slurry using gravity separation and flotation. Primary separation of the bitumen from the solids occurs in large capacity gravity settlers called primary separation vessels (PSVs), where the slurry is divided into primary bitumen froth, middlings (water, fines and bitumen) and coarse tailings (coarse solids, water, and residual bitumen). The bitumen still remaining in the middlings fraction is recovered in flotation cells where air is added and further separation of bitumen from solids occurs. The tailings that are separated are then transported to sand disposal sites.
As the mining area increases in the Fort McMurray region, the location of mining faces and the location of the sand disposal sites become more and more remote from the extraction plant. The extraction plant is comprised of a number of very large PSVs, TOR settling tanks, flotation cells, etc. Therefore, its location must remain permanent, as the equipment cannot be readily moved. Also, the cost of building new extraction plants at various other sites would be prohibitive. Therefore, slurry that is produced at a remote mine site will have to travel a great distance to the stationary extraction plant and therefore longer pipelines will be required. Further, once separation has occurred at the extraction site, the tailings will have to be transported to sand disposal sites that may also be a long distance from the extraction site. The bulk of the slurry (i.e. 50 to 60% by mass) is sand which must be transported first to extraction sites and then to disposal sites. All of this is costly. Clearly it would be much more cost effective if the sand could be separated from the conditioned slurry at a location closer to the mining site, the disposal site, or both. Therefore, a portable sand separator has been developed to separate the coarse tailings from the bitumen and middlings at a convenient location at the time. The process of removing coarse sand from an oil sand aqueous slurry is commonly referred to as "desanding".
Several factors have to be considered when developing a portable sand separator. The oil sand slurry in question, having been prepared by either of the two methods described above, is a unique feed stock. The slurry tends to be very dense (on average 1.6 sg) and contains a considerable amount of solids including rocks up to 4 inches in any dimension. Therefore, it is necessary to have a separator that can handle slurries with high concentrations of solids and large objects in both the feed and the effluent.
In addition, oil sand slurry varies with respect to its solids, water and bitumen content depending upon the oil sand grade, the process used to produce the slurry, the time of year the slurry is prepared, etc. (a slurry can contain anywhere from 50 to 65 wt % solids, 25 to 40 wt % water and 5 to 10 wt % bitumen). Therefore, it is necessary to have a separator that is capable of being controlled so that the volumetric split between the effluent (the heavy phase) and the centrate (the light phase) can be manipulated. Also, very large volumes of oil sand slurry are continuously being produced and pumped through pipelines with an inner diameter of 24 to 30 inches. Therefore, if a separator were to be hooked up directly to a pipeline, it would have to be capable of handling volumetric flow rates in the order of 25,000 to 40,000 U.S. GPM.
Finally, it is desirable that the separator be capable of separating substantially all solids larger than 44 microns or greater from the remainder of the slurry including middlings and bitumen froth.
There are no commercially available cyclonic separators that are capable of handling the large volumetric flow rates required and still reject most coarse solids. For example, there are many conical cyclonic separators on the market that are capable of removing solids as small as 44 microns. However, the flow rate range of these separators is only 200 to 1,000 U.S. GPM. Therefore, in order to accommodate the volume of slurry in question, one would have to use a cluster of such separators. For instance, if one were to use a separator with a capacity of 300 U.S. GPM, approximately 130 separators would be needed to handle 40,000 U.S. GPM of slurry. Further, the cluster would require a separate feed distributor, manifolds with shut off valves, overflow and underflow sumps and support structures with access platforms. Therefore, a complete installation of such a cluster of separators is both complex and costly.
There are other commercially available cyclonic separators that can handle larger flow rates (up to 10,000 U.S. GPM). However, these separators are unable to provide the desired separation as they can only separate out solids coarser than 150 to 250 microns. Further, these separators are not designed to handle dense slurries or handle slurries containing particles with diameters larger than 1 inch.
The use of a cyclonic separator for the separation and recovery of oil from oil sands has been previously taught. Canadian Patent No. 970,309 issued to Davitt and U.S. Pat. No. 5,316,664 issued to Gregoli et al both teach a process for recovering bitumen from tar sands using a conical hydrocyclone. However, the volume of slurry that can be accommodated by these conical hydrocyclones is limited and a series of hydrocyclones is necessary to handle the volumes in question.
In U.S. Pat. No. 2,910,424 issued to Tek et al, a conical hydrocyclone is used to separate oil from oil sands. However, in order for this hydrocyclone to work, the oil sand feed must first be comminuted in a ball mill, hammer mill, jaw crusher, etc. so that there are no large lumps and the material introduced into the hydrocyclone is composed of particles smaller than 1 mm in diameter. This design would not be capable of handling the oil sand slurries in question.